<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <style>
        .active {
            color: red;
        }
        
        li {
            cursor: pointer;
        }
    </style>
</head>

<body>
    <div id="app">
        <input id="username" type="text" value="huruqing"><br/>
        <input id="phone" type="text">
    </div>

    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
    <script>
        // 读取输入框#username的值
        var username = $('#username').val();
        console.log('username', username);

        // 设置#phone输入框的值
        $('#phone').val(13811112222);
    </script>
</body>

</html>